Force sensor and manufacture method thereof

ABSTRACT

A force sensor comprises a first substrate, a second substrate, a third substrate, and a package body. The first substrate includes a fixed electrode, at least one first conductive contact, and at least one second conductive contact. The second substrate is disposed on the first substrate and electrically connected to the first conductive contact of the first substrate. The second substrate includes a micro-electro-mechanical system (MEMS) element corresponding to the fixed electrode. The third substrate is disposed on the second substrate and includes a pillar connected to the MEMS element. The package body covers the third substrate. The foregoing force sensor has better reliability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application of U.S. patent application Ser. No.15/993,058, filed May 30, 2018 which claims benefit of China PatentApplication No. 201810391387.6 filed Apr. 27, 2018, the disclosure ofwhich is hereby incorporated by references.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a force sensor and a manufacture methodthereof, particularly to a MEMS-based force sensor and a manufacturemethod thereof.

2. Description of the Prior Art

Since the concept of the microelectromechanical system (MEMS) emerged in1970s, MEMS devices have evolved from the targets explored inlaboratories into the objects integrated with high-level systems.Nowadays, MEMS-based devices have been extensively used in consumerelectronics, and the application thereof is still growing stably andfast. A MEMS-based device includes a mobile MEMS component. The functionof a MEMS-based device may be realized through measuring the physicalmagnitude of the movement of the MEMS component. The force sensor is anexample of MEMS devices, able to detect a pressing action or a pressingforce.

The conventional force sensors include the piezoresistor type pressuresensor and the capacitor type pressure sensor. Refer to FIG. 1. In aconventional piezoresistor type pressure sensor, a plurality ofpiezoresistors 12 is disposed on a mobile membrane 11. While a pressingforce causes the mobile membrane 11 to deform, the piezoresistors 12generate corresponding signals. Refer to FIG. 2. A conventionalcapacitor type pressure sensor includes a mobile membrane 21 and a fixedelectrode 22, and the mobile membrane 21 is disposed opposite to thefixed electrode 22, whereby is formed a sensing capacitor. The signalsgenerated by the sensing capacitor are transmitted to an ApplicationSpecific Integrated Circuit (ASIC) chip 24 through a lead 23 andprocessed by the ASIC chip 24. It is easily understood: a package body25 is needed to package and protect the abovementioned components. Apressing force is conducted through the package body 25 to cause thedeformation of the mobile membrane 21 and make the sensing capacitoroutput corresponding signals.

In view of the abovementioned structures, repeated pressing actions maydegrade the reliability of the package body 25 and/or wire bondingstructure, or even damage the mobile membrane. Besides, the magnitude ofthe stress generated by pressing actions can only be controlled viamodifying the thickness of the package body 25. Thus, the force sensorsfor different scales of force are hard to be packaged with a standardpackage process. Therefore, upgrading the reliability of force sensorsand standardizing the package process has become a target themanufacturers are eager to achieve.

SUMMARY OF THE INVENTION

The present invention provides a force sensor and a manufacture methodthereof, wherein a third substrate is disposed between a package bodyand a MEMS element to function as the cover of the MEMS element, andwherein the MEMS element is connected with the cover and generates amovement corresponding to the deformation of the cover, whereby theleads inside the force sensor are far away from the stress sourcegenerated by pressing actions, and whereby the MEMS element is lesslikely to be damaged by repeated pressing actions, wherefore thereliability of the sensor is significantly increased. Besides, thepresent invention can realize force sensors of different specificationsvia merely modifying the thickness of the third substrate. Thus, theforce sensors of different specifications can be packaged in the samepackage process.

In one embodiment, the force sensor of the present invention comprises afirst substrate, a second substrate, a third substrate and a packagebody. The first substrate includes a fixed electrode, at least one firstconductive contact and at least one second conductive contact. Thesecond substrate includes a first surface, a second surface opposite tothe first surface, and a MEMS element corresponding to the fixedelectrode. The second substrate is disposed in the first substrate withthe first surface of the second substrate facing the first substrate.The first surface of the second substrate is electrically connected withthe first conductive contact of the first substrate. The third substrateis disposed in the second surface of the second substrate. The thirdsubstrate includes a pillar connected with the MEMS element. The packagebody covers the first substrate, the second substrate and the thirdsubstrate.

In one embodiment, the method for manufacturing a force sensor comprisessteps: providing a third substrate and defining at least one firstconnection member and a pillar; providing a second substrate including afirst surface and a second surface opposite to the first surface; facingthe second surface to the third substrate, and joining the secondsubstrate to the first connection member and the pillar of the thirdsubstrate; defining at least one second connection member in the firstsurface of the second substrate; defining a MEMS element in the secondsubstrate, wherein the MEMS element is connected with the pillar;providing a first substrate including a fixed electrode, at least oneconductive contact and at least one second conductive contact; joiningthe first substrate and the second substrate together, wherein the atleast one first conductive contact is electrically connected with the atleast one second connection member, and the MEMS element iscorresponding to the fixed electrode; and using a package body to coverthe first substrate, the second substrate and the third substrate.

Below, embodiments are described in detail in cooperation with theattached drawings to make easily understood the objectives, technicalcontents, characteristics and accomplishments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a conventional piezoresistortype pressure sensor;

FIG. 2 is a diagram schematically showing a conventional capacitor typepressure sensor;

FIG. 3 is a diagram schematically showing a force sensor according to afirst embodiment of the present invention;

FIG. 4 is a diagram schematically showing a force sensor according to asecond embodiment of the present invention;

FIG. 5 is a top view schematically showing a second substrate of a forcesensor according to a third embodiment of the present invention;

FIG. 6 is a diagram schematically showing a force sensor according to afourth embodiment of the present invention;

FIG. 7 is a diagram schematically showing a force sensor according to afifth embodiment of the present invention;

FIG. 8 is a diagram schematically showing a force sensor according to asixth embodiment of the present invention;

FIG. 9 is a diagram schematically showing a force sensor according to aseventh embodiment of the present invention;

FIG. 10 is a diagram schematically showing a bump of a force sensoraccording to the seventh embodiment of the present invention;

FIG. 11 is a diagram schematically showing a force sensor according toan eighth embodiment of the present invention;

FIG. 12 is a diagram schematically showing a force sensor according to aninth embodiment of the present invention;

FIG. 13 is a diagram schematically showing a force sensor according to atenth embodiment of the present invention;

FIGS. 14a-14j are diagrams schematically showing the steps pfmanufacturing the force sensor of the first embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail with embodiments andattached drawings below. However, these embodiments are only toexemplify the present invention but not to limit the scope of thepresent invention. In addition to the embodiments described in thespecification, the present invention also applies to other embodiments.Further, any modification, variation, or substitution, which can beeasily made by the persons skilled in that art according to theembodiment of the present invention, is to be also included within thescope of the present invention, which is based on the claims statedbelow. Although many special details are provided herein to make thereaders more fully understand the present invention, the presentinvention can still be practiced under a condition that these specialdetails are partially or completely omitted. Besides, the elements orsteps, which are well known by the persons skilled in the art, are notdescribed herein lest the present invention be limited unnecessarily.Similar or identical elements are denoted with similar or identicalsymbols in the drawings. It should be noted: the drawings are only todepict the present invention schematically but not to show the realdimensions or quantities of the present invention. Besides, matterlessdetails are not necessarily depicted in the drawings to achieveconciseness of the drawings.

Refer to FIG. 3. In one embodiment, the force sensor of the presentinvention includes a first substrate 31, a second substrate 32, a thirdsubstrate 33, and a package body 36. The first substrate 31 includes afixed electrode 311, at least one first conductive contact 312 and atleast one second conductive contact 313. In the embodiment shown in FIG.3, the first substrate 31 has a plurality of metal layers that areconnected with each other by interconnection structures. A portion ofthe topmost metal layer is exposed on the surface of the first substrate31 to be used as the fixed electrode 311, the first conductive contact312 and the second conductive contact 313.

The second substrate 32 has a first surface (i.e. the surface of thesecond substrate 32, which faces downward), a second surface opposite tothe first surface and a microelectromechanical system (MEMS) element323. The second substrate 32 is disposed on the first substrate 31 withthe first surface being faced to the first substrate 31 and electricallyconnected with the first conductive contact 312 of the first substrate31. For example, at least one second connection member 321 of the secondsubstrate 32 and a conductive material 322 on the terminal of the secondconnection member 321 are connected with the first conductive contact312 of the first substrate 31. The MEMS element 323 and the fixedelectrode 311 are opposite to each other to form a sensing capacitor. Itis understood that the movement of the MEMS element 323 with respect tothe fixed electrode 311 would vary the capacitance of the sensingcapacitor. Thus, a detection signal is output.

The third substrate 33 is disposed on the second surface of the secondsubstrate 32 (i.e. the surface of the second substrate 32, which facesupward). For example, the third substrate 33 is connected with thesecond surface of the second substrate 32 through a first connectionmember 331 and used as a cover of the second substrate 32. The thirdsubstrate 33 has a pillar 332 that is connected with the MEMS element323 of the second substrate 32. The package body 36 hoods the thirdsubstrate 33. For example, the first substrate 31, the second substrate32 and the third substrate 33 that have been joined together aredisposed on a package substrate 34. Next, the second conductive contact313 of the first substrate 31 and the package substrate 34 areelectrically connected with a lead 35 a by a wire bonding process. Thenthe package body 36 encapsulates the first substrate 31, the secondsubstrate 32, the third substrate 33 and the lead 35 a for protectingthe abovementioned elements. Thus, the first substrate 31 can beelectrically connected with the external device through the secondconductive contact 313 and at least one external conductive contact 341of the package substrate 34.

According to the structure shown in FIG. 3, while the third substrate 33is pressed to deform, the pillar 332 will push the MEMS element 323 tomove together with the third substrate 33. The force sensor of thepresent invention can determine whether the force sensor is pressed andthe magnitude of the pressing force via measuring the variation of thesensing capacitor. In other words, the pressing force does not directlyact on the MEMS element 323 of the present invention so as not to dodamages on the MEMS element 323 by repeated pressing actions. Besides,as shown in FIG. 3, the arrangement that pressing action puts force onthe third substrate 33 makes the lead 35 a far away from the stresssource of pressing action so as to significantly increase thereliability of the wire bonding structure and the force sensor of thepresent invention. It is noted that the range of measured force can beadjusted via modifying the thickness of the MEMS system 323, the designof the elastic arm of the MEMS element 323 or the material/thickness ofthe package body. Further, the range of measured force, such as 10newtons or 100 newtons, can be adjusted via modifying the thickness ofthe third substrate. Therefore, the force sensors for measuringdifferent ranges of force can be packaged with the same package process.

In one embodiment, the first substrate 31 includes a driver circuitand/or a sensing circuit. For example, the first substrate 31 may havean analog and/or digital circuit, which is normally realized by anApplication Specific Integrated Circuit (ASIC). However, the presentinvention is not limited by the abovementioned embodiment. In oneembodiment, the first substrate 31 is also called the electrodesubstrate. For example, the first substrate 31 may be a substrate havingappropriate rigidity, such as a complementary metal oxide semiconductor(CMOS) substrate or a glass substrate. Refer to FIG. 4. In theembodiment shown in FIG. 4, the force sensor of the present inventionfurther comprises an ASIC chip 37. In the embodiment shown in FIG. 4,the first substrate 31 is stacked on the ASIC chip 37; the secondconductive contact 313 of the first substrate 31 is electricallyconnected with the ASIC chip 37 through the lead 35 a, and the ASIC chip37 is further electrically connected with the package substrate 34through a lead 35 b. Via the abovementioned structure, the firstsubstrate 31 can be electrically connected with an external devicethrough the second conductive contact 313, the ASIC chip 37, and theexternal conductive contact 341 of the package substrate 34. It isunderstood that the force sensor of the present invention may beimplemented by the case that the first substrate 31 and the ASIC chip 37are disposed on the same plane side by side.

Refer to FIG. 3 again. In one embodiment, the first substrate 31 furtherincludes at least one reference electrode 314, and the second substrate32 further includes at least one reference element 324; the referenceelectrode 314 and the reference element 324 are opposite to each otherto form a reference capacitor. The reference capacitor and the sensingcapacitor jointly form a differential capacitor pair, whereby to improvethe precision of measurement. It is noted that the reference element 324of the second substrate 32 is a fixed element, as shown in FIG. 3.However, the present invention is not limited by the abovementionedembodiment. In one embodiment, the reference element 324 is a movableelement, as shown in FIG. 5. In the embodiment shown in FIG. 5, the MEMSelement 323 and the reference element 324 of the second substrate 32form a seesaw structure with the second connection member 321 being theanchor point. According to the abovementioned seesaw structure, whilethe MEMS element 323 is moved downward by the pressing stress, thereference element 324 is moved upward. Therefore, a tiny magnitude ofmovement can be measured using the difference between the capacitancevariation of the sensing capacitor and the capacitance variation of thereference capacitor. Thus is increased the precision of measurement.

Refer to FIG. 6. In one embodiment, the package body 36 includes aprotrusion 361. The protrusion 361 is corresponding to the MEMS element323. In other words, the protrusion 361 is corresponding to the thirdsubstrate 33, and more exactly, corresponding to the pillar 332 of thethird substrate 33. The assemblage errors may result in differentmeasurement errors. The protrusion 361 concentrates the pressing forcethereon, whereby the force sensor of the present invention still outputsmore consistent measurement results under different assemblage errors.

Refer to FIG. 7. In one embodiment, the force sensor of the presentinvention further includes a protrudent member 38 disposed on thepackage body 36. The protrudent member 38 has a bump 381 that iscorresponding to the MEMS element 323. Similar to the protrusion 361 ofthe package body 36, the bump 381 protrudes from the package body 36 andconcentrates the pressing force thereon so as to allow the force sensorof the present invention to tolerate a larger range of assemblage error.In the embodiment shown in FIG. 7, the top surface of the bump 381 is aplane. However, the present invention is not limited by the embodiment.Refer to FIG. 8. In one embodiment, the top surface of the bump 381 is acurved face. It is understood that the bump 381 can be attached to thepackage body 36 by an adhesive 39.

Refer to FIG. 9. In one embodiment, the protrudent member 38 has a bump381 and a plate 382, wherein the plate 382 is arranged between the bump381 and the package body 36. In one embodiment, the bump 381 and theplate 382 of the protrudent member 38 are fabricated into a one-piececomponent. In one embodiment, the bump 381 and the plate 382 are made ofa metallic material. The projection area of the plate 382 is smallerthan or equal to the area of the third substrate 33. In the embodimentshown in FIG. 9, the plate 382 is corresponding to the deformed area ofthe third substrate 33. Refer to FIG. 10. In one embodiment, theprojection area of the plate 382 is larger the area of the thirdsubstrate 33 and covers the upper surface of the package body 36.Similarly, the top surface of the bump 381 may be a plane (as shown inFIG. 9) or a curved surface (as shown in FIG. 10). It should be furthermentioned herein: the thickness of the plate 382 can also be used tocontrol the measurement range of the force sensor of the presentinvention.

Refer to FIG. 11 and FIG. 12. In one embodiment, the plate 382 isdisposed above the bump 381. In other words, the bump 381 is arrangedbetween the plate 382 and the package body 36. In such a structure,while the plate 382 is pressed, the stress is concentrated on the bump381. Thus is further increased the tolerance of the force sensor of thepresent invention to the assemblage errors. In one embodiment, the plate382 has at least one connection leg 383. The connection leg 383 isjoined with the package body 36 to prevent the plate 382 from beingtilted by pressing actions.

Refer to FIG. 13. In one embodiment, the bump 381 is formed via aglue-dispensing method. It is understood that the bump 381 is made of apolymeric material in this embodiment.

Refer to FIGS. 14a-14j for the description of the manufacture method ofthe force sensor of the present invention shown in FIG. 3. Only a singledevice is shown in these drawings. However, it is understood that aplurality of devices may be fabricated on a single substrate, and thesingle device shown in these drawings is only an exemplification; thepresent invention is not limited by the exemplification. Thespecification will further describe the method of using a wafer-scaleprocess to fabricate a plurality of chips or devices on a substrate.After the devices have been fabricated on a substrate, a dicingtechnology or a singulation technology will be used to generateindividual devices, and the individual devices will be packagedseparately for applications.

Refer to FIG. 14 a. Firstly, a third substrate 33 is provided and atleast one first connection member 331 and a pillar 332 in the thirdsubstrate 33 are defined. In one embodiment, the third substrate 33 isetched to form a plurality of trenches 333, whereby to define the firstconnection member 331 and the pillar 332.

Refer to FIG. 14 b. Next, a second substrate 32 is provided to include afirst surface 32 a and a second surface 32 b opposite to the firstsubstrate 32 a. The second surface 32 b of the second substrate 32 isfaced to the third substrate 33, and then the second surface 32 b isjointed to the first connection member 331 and the pillar 332 of thethird substrate 33. In one embodiment, the second substrate 32 and thethird substrate 33 are joined together in a fusion bond method. In oneembodiment, after the second substrate 32 and the third substrate 33have been joined together, the second substrate 32 is thinned. In oneembodiment, the second substrate 32 is thinned to have a thickness ofequal to or smaller than 30 μm.

Refer to FIG. 14 c. Next, at least one second connection member 321 onthe first surface 32 a of the second substrate 32 is defined. Refer toFIG. 14 d. In one embodiment, according to the method of joining thesecond substrate 32 and a first substrate 31 in the subsequent step, anappropriate joining material is formed on the second connection member321. In one embodiment, the joining material is a conductive material322.

Refer to FIG. 14 e. Next, a MEMS element 323 in the second substrate 32is defined. It is noted that the MEMS element 323 of the secondsubstrate 32 must be joined to the pillar 332 of the third substrate 33.In one embodiment, at least one reference element 324 is definedsimultaneously while the MEMS element 323 is defined.

Refer to FIG. 14 f. Next, a first substrate 31 is provided to include afixed electrode 311, at least one first conductive contact 312 and atleast one second conductive contact 313. In one embodiment, the firstsubstrate 31 also includes a reference electrode 314.

Refer to FIG. 14 g. Next, the first substrate 31 is jointed to thesecond substrate 32, wherein the first conductive contact 312 of thefirst substrate 31 is electrically connected with the second connectionmember 321 of the second substrate 32 through the conductive material322, and wherein the MEMS element 323 is corresponding to the fixedelectrode 311. In one embodiment, the second substrate 32 is joined tothe first substrate 31 in at least one of an eutectic bonding method, afusion bond method, a soldering method and an adhesive method.

Refer to FIG. 14 h. Next, the third substrate 33 is thinned to have anappropriate thickness. Refer to FIG. 14 i. Next, a portion of the thirdsubstrate 33 is removed to expose the second conductive contact 313 ofthe first substrate 31. Next, the first substrate 31 is diced for thesubsequent package process. Refer to FIG. 14 j. In one embodiment, thesingulated first substrate 31 is placed on a package substrate 34, anduse a lead 35 a to electrically connect the second conductive contact313 of the first substrate 31 to the package substrate 34. Then, apackage body 36 is used to cover the third substrate 33 to form theforce sensor shown in FIG. 3. It is understood that an appropriate moldcan be used in a molding package process to form the protrusion 361shown in FIG. 6.

In the present invention, the force sensors with different packagedesigns are realized in different package processes. For example, inpackaging the force sensor shown in FIG. 4, the first substrate 31 isdisposed on the ASIC chip 37; next, at least one second conductivecontact 313 of the first substrate 31 is electrically connected with theASIC chip 37 through the lead 35 a; then, the package body 36 is used tocover all the elements. In one embodiment, the force sensor of thepresent invention and the ASIC chip are disposed on the packagesubstrate side by side; then, wire bonding and molding package areundertaken to complete the sensor.

In one embodiment, the manufacture method of the force sensor of thepresent invention further includes a step of forming a protrudent member38 having a bump 381 on the package body 36, as shown in FIGS. 7-12. Inone embodiment, the bump 381 is formed on the package body 36 in aglue-dispensing method, as shown in FIG. 13.

In conclusion, the present invention proposes a force sensor, wherein athird substrate is disposed between a package body and a MEMS element tofunction as the cover of the MEMS element, whereby the MEMS element isspatially separated from the package body. The MEMS element is connectedwith the cover and generates a movement corresponding to the deformationof the cover. Thereby, the leads inside the force sensor are far awayfrom the stress source generated by pressing actions, and the MEMSelement is less likely to be damaged by repeated pressing actions. Thus,the reliability of the sensor is significantly increased. Besides, thepresent invention can realize force sensors of different specificationsvia merely modifying the thickness of the third substrate. Therefore,the force sensors of different specifications can be packaged in thesame package process.

What is claimed is:
 1. A method for manufacturing a force sensor,comprising: providing a third substrate and defining at least one firstconnection member and a pillar in the third substrate; providing asecond substrate including a first surface and a second surface oppositeto the first substrate; facing the second surface to the third substrateand joining the second substrate to the first connection member and thepillar of the third substrate; defining at least one second connectionmember in the first surface of the second substrate; defining a MEMSelement in the second substrate, wherein the MEMS element is connectedwith the pillar; providing a first substrate including a fixedelectrode, at least one first conductive contact and at least one secondconductive contact; joining the first substrate to the second substrate,wherein the at least one first conductive contact is electricallyconnected with the at least one second connection member, and whereinthe MEMS element is corresponding to the fixed electrode; and using apackage body to cover the first substrate, the second substrate and thethird substrate.
 2. The method for manufacturing a force sensoraccording to claim 1 further comprising thinning the third substrate. 3.The method for manufacturing a force sensor according to claim 1 furthercomprising thinning the second substrate.
 4. The method formanufacturing a force sensor according to claim 1 further comprisingforming a conductive material on the second connection member.
 5. Themethod for manufacturing a force sensor according to claim 1, whereinthe first substrate includes at least one reference electrode, and thesecond substrate includes at least one reference element correspondingto the reference electrode.
 6. The method for manufacturing a forcesensor according to claim 5, wherein the at least one reference elementis a fixed element.
 7. The method for manufacturing a force sensoraccording to claim 5, wherein the at least one reference element is amovable element.
 8. The method for manufacturing a force sensoraccording to claim 1, wherein the first substrate includes acomplementary metal oxide semiconductor (CMOS) substrate.
 9. The methodfor manufacturing a force sensor according to claim 1, wherein the firstsubstrate includes an application specific integrated circuit (ASIC).10. The method for manufacturing a force sensor according to claim 1further comprising: disposing the first substrate on an ASIC chip ordisposing the first substrate beside the ASIC chip on the same plane;and using a lead to electrically connect the at least one secondconductive contact with ASIC chip.
 11. The method for manufacturing aforce sensor according to claim 1, wherein the package body includes aprotrusion corresponding to the MEMS element.
 12. The method formanufacturing a force sensor according to claim 1 further comprisingdisposing a protrudent member on the package body, wherein theprotrudent member includes a bump corresponding to the MEMS element. 13.The method for manufacturing a force sensor according to claim 12,wherein a top surface of the bump is a plane or a curved surface. 14.The method for manufacturing a force sensor according to claim 12,wherein the bump is made of a metallic material or a polymeric material.15. The method for manufacturing a force sensor according to claim 12,wherein the protrudent member includes a plate disposed between the bumpand the package body or disposed above the bump.
 16. The method formanufacturing a force sensor according to claim 15, wherein a projectionarea of the plate is smaller than or equal to an area of the thirdsubstrate.
 17. The method for manufacturing a force sensor according toclaim 15, wherein the plate is disposed between the bump and the packagebody and covers the package body.
 18. The method for manufacturing aforce sensor according to claim 15, wherein the plate is disposed abovethe bump and includes at least one connection leg connected with thepackage body.